This document discusses the physiology of hypoxia, or reduced oxygen supply to tissues. It defines four types of hypoxia: hypoxic (reduced oxygen in arterial blood), anemic (decreased blood's oxygen carrying capacity), stagnant (decreased blood flow to tissues), and histotoxic (tissues' decreased ability to use oxygen). For each type, it outlines the characteristic arterial oxygen levels, oxygen saturation, and other features, as well as potential causes. The effects of hypoxia depend on its severity, duration, and type, but can include symptoms like cyanosis, tachycardia, tachypnea, and metabolic acidosis. Over time, the body may compensate through mechanisms like angiogenesis and polycythemia.

1. Physiology of hypoxia

2. Definition
▪ Reduced oxygen supply to the tissues

3. Classification
▪ Reduced oxygen tension of arterial blood – Hypoxic hypoxia
▪ Decreased oxygen carrying capacity of the blood – anemic hypoxia
▪ Decreased rate of blood flow to the tissues – stagnant hypoxia
▪ Decreased utilization of oxygen by tissues – histotoxic hypoxia

4. But first
▪ Arterial Po2
▪ Oxygen carrying capacity of blood (Hb value )
▪ A –V difference of Po2
▪ Percentage saturation of hemoglobin SaO2

5. Hypoxic hypoxia
▪ Decreased oxygen tension in blood
▪ Decreased O2 saturation of blood
▪ O2 carrying capacity of blood is normal
▪ Blood flow to the tissues normal
▪ Tissue utilization is normal
▪ A –V Po2 difference is low

6. Causes
▪ Low oxygen tension of inspire air
– High altitude
– Closed spaces
– Artificial gas breathing
▪ Hypoventilation
– Obstruction to respiratory passages
– Decreased lung compliance
– Paralysis of respiratory muscles
– Respiratory depression
▪ Reduced diffusion of O2 across respiratory membrane
– Emphysema , pulmonary edema , fibrosis

7. Anemic hypoxia
▪ Basic problem is decreased oxygen carrying capacity of blood
▪ Causes
– Anemia – bone marrow depression
– CO poisoning
– Met-haemoglobinemia

8. Characteristic features
▪ Arterial Po2 is normal
▪ O2 carrying capacity of blood is reduced ( SaO2 reduced)
▪ A –V difference is normal
▪ Normal tissue utilization

9. 2,3 DBG significance
▪ Increases O2 delivery to tissues
▪ Hbo2 + 2, 3 DBG Hb 2, 3 DBG + O2

10. Stagnant hypoxia
▪ Problem – decreased blood flow to tissues (stagnation)
▪ Normal Po2 , SaO2 , Hb , normal tissues
▪ Causes – generalized , localized
– Shock , CHF
– Thrombosis , embolism, atherosclerosis

11. Characteristic Features
▪ Normal pO2
▪ Normal SaO2
▪ A –V pO2 is high than normal

12. Histotoxic Hypoxia
▪ Problem with tissues
▪ Tissues not able to use the oxygen
▪ Inhibition of cellular respiration (ETC) by poisons
▪ Cyanide , sulphide poisoning
▪ Normal pO2
▪ SaO2 normal
▪ A –V difference is nil

13. Effects of hypoxia
▪ Hypoxia mainly affects CNS , specially the higher centers
▪ Fulminant hypoxia , acute hypoxia , chronic hypoxia
▪ Effects depends on the severity , duration and type , and
compensatory mech of body

14. Important Symptoms And Signs
▪ Cyanosis
▪ Tachycardia
▪ Tachypnoea
▪ Acute hypoxia resembles alcohol intoxication
▪ Anaerobic glycolysis
▪ Metabolic acidosis with respiratory alkalosis
▪ Angiogenisis
▪ Polycythemia
▪ Pulmonary hypertension